Determination of optimal timing window for pulmonary artery MDCT angiography

OBJECTIVE. The purpose of our study was to determine the optimal timing window for pulmonary artery MDCT angiography. SUBJECTS AND METHODS. We prospectively studied 150 patients. Routine chest CT scans were acquired using 1.3 mL/kg of contrast medium ( 370 mg I/mL) that was injected at a fixed injection duration of 30 seconds, followed by a 10-second saline chase. To measure early contrast enhancement, sequential monitoring scans were obtained every 2 seconds over a fixed level of the main pulmonary artery 5 seconds after the start of the injection. Then helical diagnostic scans were obtained at three different predetermined scanning delays ( group A, 25 seconds; group B, 35 seconds; and group C, 45 seconds after the start of the injection). Time - enhancement curves; time to reach 100 H, 200 H, and peak enhancement; and enhancement duration greater than 200 H of the pulmonary artery were measured from the monitoring scan. Contrast enhancements of the pulmonary artery and descending aorta and vascular artifacts were assessed from the diagnostic scan. RESULTS. Times to reach 100 H and 200 H at the pulmonary artery were mean 11 +/- 2.5 (SD) seconds and 16 +/- 3.0 seconds, respectively. Pulmonary artery enhancement duration of greater than 200 H was 25 +/- 2.7 seconds ( only obtained in group C). Mean time to peak enhancement ( 335 +/- 62 H) at the pulmonary artery was 37 seconds. Mean enhancement measured on the diagnostic scan was 294 +/- 43 H, group A; 208 +/- 48 H, group B; and 157 +/- 15 H, group C for the pulmonary artery, and 240 +/- 42 H, group A; 277 +/- 49 H, group B; and 172 +/- 29 H, group C for the aorta ( p < 0.01). Artifacts were noted in the superior vena cava ( group A, 96.7%; group B, 18.3%; and group C, 0%) and in the subclavian vein ( group A, 93.5%; group B, 38.7%; and group C, 0%), ( p < 0.05). CONCLUSION. With our study protocol of a 30-second injection and 10-second saline flush, the optimal temporal window to achieve pulmonary artery enhancement greater than 200 H was from 16 seconds to 41 seconds after the start of the injection.